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Useful Notes / Tyrannosaurus rex

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"Sue" on display at the Field Museum of Natural History in Chicago, Illinois. Photographed by Evolutionnumber9 and licensed under CC BY-SA 4.0.
There's no doubt that Tyrannosaurus rex is, by far, the most famous of the Stock Dinosaurs, seen as both the most majestic and most terrifying of them. However, there are lots of common misconceptions about the animal, which we attempt to clear up here.

  • Name: Whereas most dinosaurs are known outside paleontological circles only by their genus, T. rex is known by their full binomium. Tyrannosaurus, the genus name, comes from the Greek tyrannos, meaning "tyrant", and sauros, meaning "lizard". Rex, the specific name, meanwhile, is Latin for "king", therefore the whole name translates to "tyrant lizard king". As per the rules of binomial nomenclature, the genus name should be spelled with a capital T, whereas the species name should be spelled with a lowercase r. And the correct abbreviation of the name is T. rex, not T-rex and especially not T-Rex. The word "tyrannosaur" refers to any member of the family Tyrannosauridae, which, beside T. rex, also includes Tarbosaurus (once sometimes considered the Asian Tyrannosaurus species), Albertosaurus, Gorgosaurus, Yutyrannus and many more. Early fossils were described under the names Dynamosaurus imperiosus and Manospondylus gigas - both of them are now considered invalid synonyms. A number of other names have also become invalid synonyms of Tyrannosaurus over the years, including Nanotyrannus, Stygivenator and Alamotyrannus.
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  • Discovery: The first T. rex fossils were found in the late 1800s and were believed to belong to a giant ornithomimid or a ceratopsid. The species was officially described by Henry Farfield Osborn in 1905, based a partial skeleton consisting of 34 bones, found by curator Barnum Brown in Hell Creek, Montana. Osborn described another fossil of a large carnivore, found in Wyoming, as Dynamosaurus imperiosus, but then realized that the two belonged to the same species. The most complete T. rex skeletons were found in 1990 and 1992, and were dubbed as "Sue" and "Stan". These two fossils helped us get a much more accurate image of what the species was like.
  • Time period: T. rex lived at the very end of the Cretaceous period, 68-66 million years ago (also known as the Maastrichtian age). It was among the few dinosaurs that was still around when the famous asteroid collision ended the Mesozoic era (others included Triceratops, Ankylosaurus and Edmontosaurus). Any depiction of T. rex earlier than that is, therefore, inaccurate.
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  • Range: T. rex was an exclusively North American species. During the Late Cretaceous, North America was divided to two smaller continents by a shallow sea named the Western Interior Seaway; T. rex lived on the Western continent, dubbed Laramidia. It was found throughout Laramidia, ranging from Alberta in the north to Texas and New Mexico in the south. A closely related species, the aforementioned but smaller Tarbosaurus bataar, lived in East Asia at the same time.
  • Size: T. rex was famous for being one of the largest carnivorous dinosaurs. The "Sue" skeleton is 12.3 to 12.8 m long (the inaccuracy comes from a few missing vertebrae), about 4 m tall at the hip, and is estimated to weigh 8.4 to 14 metric tons (for comparison, that's 2 to 3 times the weight of an African bush elephant).
  • Posture: Early restorations depicted T. rex in a kangaroo-like tripod posture, dragging its long tail on the ground. However, thanks to more complete skeletons, now we know that it held its body horizontally, balancing its body with its tail.
  • Big head: T. rex had a massive head even in comparison to other carnivorous dinosaurs. Its mouth was full of sharp teeth, up to 20 cm (8 inches) long, sometimes dubbed "killer bananas" because of their size and shape. Its bite force is estimated to be about 8,000 pounds, stronger than any other known land animal, which it needed to crush the bones of the large dinosaurs it ate.
  • Puny arm: One of the most iconic, and most ridiculed, traits of T. rex is its tiny arm. It was two-fingered, with sharp claws on them, and its palms faced inward (rather than downward, as it's often erroneously depicted). The reason for the arms's small size is mainly practicality; large arms would have gotten in the way of the Tyrannosaurus's bite, which is theorized to have been the most powerful bite of all dinosaurs, hence the need to have small arms where other predators would have clawing weapons. Additionally, in spite of their size the arm bones show signs of large muscle attachment and thus, they were very strong and capable of lifting 200 pounds (90 kilograms). Because of this, T. rex might have used them to hold onto struggling prey while it dispatched it with its jaws. In addition, they could have also been used to help lift the T. rex from a sleeping position when it was waking up.
  • Hunter or scavenger: Though the T. rex is typically portrayed as a hunter in media, there was an infamous debate among paleontologists as to whether or not T. rex was actually a scavenger instead, popularized by paleontologist and Jurassic Park dinosaur consultant Jack Horner. While the idea of a large, bulky carnivore solely surviving on rotting carrion is just too ridiculous to be taken seriously (due to the amount of food needed to sustain its massive size), it is theorized that large, adult Tyrannosaurus would hunt less and basically Kill Steal the hunts of other carnivores and younger T. rex; the highly advanced olfactory sense of the creature allowed it to sniff out carrion from miles away, and a roar would have definitely helped scare off smaller dinosaurs from a kill. Due to an adult's size and strength, however, it's also very possible that it simply fought animals like Triceratops or Ankylosaurus and wonnote , whereas younger, smaller Tyrannosaurus hunted hadrosaurs note  the old fashioned way. Even in that case, a roar could've been helpful; even the most active predators are unlikely to pass up the opportunity to steal a free meal if they can, and a Tyrannosaurus might well have needed to threaten off other dinos (including other Tyrannosaurus) while eating.
  • Feathers or scales: Historically, T. rex was portrayed with lizard- or crocodile-like scaly skin. However, as many dinosaur species were discovered to be covered in feathers, including another tyrannosaur, Yutyrannus, it was suggested that T. rex could also have been feathered, basically looking like a giant toothy bird. However, fossilized skin impressions of T. rex and other, closely related tyrannosaurs show that most of its body was, indeed, scaly; the only place that was potentially feathered is its back. As T. rex was a large animal living in warm climate, it likely did not need the extra insulation from feathers, just as similarly-sized mammals like rhinoceroses and elephants are sparsely haired. However, some still speculate that it had downy feathers as a hatchling, when it was still small enough to need insulation, and eventually lost these as it reached a certain age and size.
  • Sound: T. rex is typically depicted in media with a Mighty Roar; ever since Jurassic Park, everyone knows what that roar sounded like. However, there is actually little evidence that T. rex could roar; it is speculated to have produced low-pitched, rumbling or bellowing sounds, similar to crocodilians.
  • Senses: T. rex had extraordinary senses of smell and hearing. Analysis of the braincase in fossilized skulls shows that it had large olfactory bulbs and a long cochlear duct capable of receiving low-frequency sounds. These traits would have been advantageous both as a predator (hunting prey) and as a scavenger (finding carrion from a great distance or detecting approaching rivals). However, contrary to what Steven Spielberg and Michael Crichton would have you believe, T. rex also had excellent eyesight that would've let the creature spot objects from as far as six kilometres with thirteen times the detail. It had large eyes facing forward connecting to big optical lobes, and a relatively narrow snout, allowing for binocular vision. This ability supports the idea that T. rex was a hunter, as binocular vision is beneficial when chasing prey.

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